JEFFERSON CITY, Mo. — A measure headed to President Donald Trump's desk could help World War II veterans exposed to mustard gas by the military, Missouri Sen. Claire McCaskill said Thursday.

The measure, which the Senate passed as part of another bill to expand college aid for military veterans, would require the Veterans Affairs Department to reconsider disability benefits denied to those who claimed the testing caused health problems.

McCaskill said the military tested the effects of mustard gas and the blister agent lewisite on about 60,000 veterans by the end of World War II. Her office estimates a couple hundred participants could still be alive, including 90-year-old Missouri resident Arla Harrell, for whom the bill was named.

"It says to Arla Harrell, 'We believe you,'" McCaskill said. "And that is a very important thing to say to Arla and other men like him who were willing to give the ultimate sacrifice for their country."

Harrell's daughter, Beverly Howe, says he had mustard agents dabbed on his skin and was placed in a gas chamber without protections in southwestern Missouri's Camp Crowder after he enlisted in the Army in 1945. He's since had lung issues and skin cancer, but has been denied benefits. He and other veterans were sworn to secrecy until 1991, complicating efforts to get benefits.

"When these men were released from this vow of secrecy, our country did not stand up at that point and say, 'We got it. We've got your back,'" Howe said. "That's where I find the moral ground for me."

If signed by Trump, the legislation will require the Veterans Affairs Department to assume those who served at sites where McCaskill's office says testing occurred and are trying again to get benefits are telling the truth and would need to prove otherwise. Other provisions would require investigations by the Veterans Affairs and Defense departments.

McCaskill says the policy change is estimated to cost about $9 million over the next 10 years.